1. Field of the Invention
The present invention pertains to, among optical systems in cameras, etc., compact optical systems that have a high decentering error sensitivity and that require assembly in which lens positions are adjusted.
2. Description of the Related Art
Conventionally, assembly of a lens into a lens holder has generally been performed by inserting the lens into a lens holder having an inner diameter equal to or slightly larger than an outer diameter of the lens, tightening the holder around the lens and fixing the assembly using a spring washer or an adhesive. While this method allows easy assembly and inexpensive processing of the components, it has the problem that the lens easily becomes decentered relative to the optical axis and the lens therefore cannot be precisely maintained in the correct position. If the lens becomes decentered relative to the optical axis, decentering aberrations such as axial coma and curvature of field asymmetricity occur due to errors resulting from the decentering, and consequently the conventional assembly of a lens into a lens holder has been a major cause of deterioration in optical performance.
Meanwhile, in optical systems having a high error sensitivity for axial coma, a lens position adjustment device having a lens position adjusting means has been developed that detects the axial coma from the light that has passed through the optical system and adjusts the position of one lens such that the axial coma is reduced to the minimum, and lenses and lens holders have been assembled using this device. This device has played the role of reducing the axial coma of one lens block in the entire optical system to the minimum by adjusting the relative position of a certain lens. (U.S. Pat. No. 5,453,606).
However, in the trend toward increasingly small optical systems witnessed in recent years, the decentering error sensitivity has been increasing not only in one lens block but also between lens blocks, and the problem has arisen that, due to significant decentering aberrations, the desired optical performance cannot be attained simply by assembling the lens blocks without any further adjustment. In addition, in the past, the curvature of field asymmetricity could be reduced to a certain extent in many optical systems by eliminating the axial coma, but currently an increasing percentage of optical systems have an error sensitivity characteristic such that the curvature of field asymmetricity remains even if the axial coma is eliminated.
In other words, because the decentering error sensitivity of each lens block has increased due to the reduction in size of optical systems, the desired performance cannot be achieved using the conventional assembly method, and resolution of this problem is seen as a major issue.